Compact lasers that are commercially available are semiconductor lasers that rely upon photon generation in a solid in response to electrical current. These lasers come in various forms and find many applications although II-VI compound semiconductors have also lased. They are generally fabricated in the Group III-V materials systems. Although semiconductor lasers and laser bars are capable of generating continuous power outputs in the kW range and above, the peak power output available with such lasers is generally low. In particular, semiconductor lasers are not capable at present of providing pulsed visible or ultraviolet (UV) radiation at high peak power (kW and above). Furthermore, semiconductor lasers generally produce output beams of poor quality that are highly divergent and require external collimation. When higher power beams are required, large and expensive gas, chemical, solid state (non-semiconductor), or excimer lasers are typically used.
University of Illinois researchers have led the development of microcavity plasma devices. United States Published Application 2007-0200499, entitled Polymer Microcavity and Microchannel Devices and Fabrication Method and published Aug. 30, 2007, discloses microcavity plasma device arrays formed in polymers, and also discloses high aspect ratio microchannels in which plasma can be formed. Arrays disclosed in that application can have high aspect ratio microchannels that are disclosed as connecting microcavities, and also as being formed into patterns having a wide variety of shapes, e.g., straight, zig-zig and other shapes. Very long, high aspect ratio channels are disclosed, e.g., a one meter channel that is 100 μm wide, yielding an aspect ratio of 10,000:1.
Other work by University of Illinois researchers has provided microcavity plasma devices with tapered microcavities, as disclosed in Eden et al., is U.S. Pat. No. 7,112,918, which issued Sep. 26, 2006. The tapered microcavities could be formed by micromachining, drilling and other semiconductor fabrication techniques, in semiconductor materials. By a preferred wet chemical semiconductor etch, the taper is caused by a difference in the etch rates of the etchant along the different crystalline planes of the semiconductor being etched. The shape of the cavities in the '918 patent when etching is used is also dependent on the semiconductor material used due to the disparity in the etch rates along the different crystalline planes in different material systems. Semiconductor photolithographic and etching processing techniques are disclosed as being a convenient and inexpensive way to form tapered microcavity plasma devices.